1. Technical Field
The present invention relates to cooling fans, and more particularly to an impeller of a cooling fan which helps to decrease noise generated by the cooling fan when the cooling fan is operated.
2. Description of Related Art
It is well known that heat is produced by electronic components such as central processing units (CPUs) during their normal operations. If the heat is not timely removed, these electronic components may overheat. Therefore, heat sinks and cooling fans are often used to cool these electronic components.
Generally, a cooling fan includes an enclosure, a stator received in the enclosure and an impeller being rotatable with respect to the stator. The impeller includes a hub and a plurality of blades radially and outwardly extending from the hub. When the cooling fan operates, the blades of the impeller rotate around the stator to drive an airflow to flow towards an electronic component, thus cooling the electronic component continuously. Increasing revolving speed of the impeller relatively increases the amount of the airflow, and therefore a heat dissipation efficiency of the cooling fan is relatively improved. However, increasing the revolving speed may correspondingly cause a rise of a noise level generated by the cooling fan, thus making a user near the cooling fan feel uncomfortable.
When a flow field of the cooling fan is simulated by a computational fluid dynamics software, it is found that one of the reasons for increase of the noise is a superposition of a plurality of high harmonic waves in a chamber defined between every two adjacent blades of the impeller. What is needed, therefore, is an impeller and a cooling fan incorporating the impeller which has a low operating noise.